Capacitive-Controlled Oscillator (CCO) based "capaciflector" proximity sensors and CCO based sensor arrays are available (see FIG. 1a and U.S. Pat. No. 5,166,679 for a discussion of the basic "capaciflector" technology). However, CCO based "capaciflector" sensors can be used as arrays only where the separation between individual sensors can be made large, such as 3 to 6 inches. Also, for a "capaciflector" sensor to perform efficiently, the shield must be much larger that the sensor (on the order of 7 times wider) and each sensor must have its own shield. The shield is slaved to the sensor via a voltage follower, so it changes frequency with the sensor. If another sensor is introduced, another CCO and voltage follower shield must be added. Hence, the sensors must be spaced no closer than the width of the shields. Even then, there is some cross talk because the two sensors are out of phase with each other. This application is satisfactory for collision avoidance arrays and rudimentary alignment, but an entirely new approach is necessary for a "capaciflector" camera.
Tactile capacitive arrays using pixels are also available in the research environment and appear to be practical for medical and industrial applications. However, these devices have such a short range that they would not have the depth of view necessary for good capacitive 3-D proximity images and they would be impractical for robotic collision avoidance purposes (frequently part of the "capaciflector" camera imaging function). Also, without the current-measuring voltage follower electronics architecture described in this disclosure (and an active current bridge version of the same), there will be cross talk between the pixels and/or their leads.
"Capaciflector" 3-D imaging using a single sensor has also been achieved in the prior art. In this application, the single "capaciflector" sensor is moved through a volume with sensor readings being taken sequentially in the process. These readings are compared with the robot joint angles and a 3-D image results. There are three disadvantages to this type of system; first, large volumes often must be swept out in order to obtain a complete picture and this may not be possible or practical in a docking or berthing application; second, the process takes a considerable amount of time; and third, the measurements must be correlated with robot joint angle information which introduces further inaccuracies.